Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
Hi

Many contributors and readers of this forum will be familiar with D. Selfs writing (and those who are not should take actions to get!). In particular his audio power amplifier design handbook is already a classic. I did put together a paper with a couple of complementing and contrasting thoughts on the 5th edition. I hope you enjoy reading it and appreciate further conversation on the topics covered.

audio_power_amp_design_comments.pdf

Samuel


JohnRoberts

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #1 on: February 14, 2011, 10:39:55 AM »
Very Impressive... Looks like you invested a lot of hours and thought into your analysis.

I recognized many old classics in your footnotes. I didn't see Cherry. I though he had a few interesting AES papers. IIRC in one he investigated how things like path impedance for power supply rail feeds and returns affect distortion in high power output stages. When investigating residuals as low as you are, there are many moving parts to consider.

Good work... I fear that analog design is a fading specialty as it becomes easier to just plug in ICs to accomplish most tasks (of course somebody must design those ICs and that may be where the heavy lifting occurs in the future). I hope your work encourages others to follow you down that path. Not that we need to design a lot of discrete amplifiers, just so we know how to. 

I recall an old science fiction story about some time in the future when a historian discovers the ancient practice of math. Long since forgotten by the public, due to lack of use.  :D

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

EmRR

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #2 on: February 14, 2011, 02:40:37 PM »
Looks deep; adding to the pile.  Thanks for sharing.
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

sahib

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #3 on: February 14, 2011, 04:29:24 PM »
Sam, for some reason I can not open your link. I saved the pdf onto my desktop but still it won't open. Any advice would be appreciated.

clintrubber

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #4 on: February 14, 2011, 04:50:59 PM »
Thanks for sharing. Can well imagine you sent your points to him as well, right ?
If so, please keep us informed about what you want to share of the subsequent discussion.

Regards

Michael Tibes

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #5 on: February 14, 2011, 04:53:02 PM »
Looks deep; adding to the pile.  Thanks for sharing.
Seems fine here now...

Michael

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #6 on: February 15, 2011, 09:21:33 AM »
Thanks for your interest!

Quote
Sam, for some reason I can not open your link.

With a slow connection it might take a while, almost 1 MB. Other than that, I see no reason why it should not work--which Acrobat Reader version do you use? Have you tried copy the URL and pasting to a new browser window/tab?

You could also try the link from here: www.sg-acoustics.ch/analogue_audio/power_amplifiers/

Quote
Can well imagine you sent your points to him as well, right? If so, please keep us informed about what you want to share of the subsequent discussion.

It is of course not only my decision what shall not be private anymore from a privat communication...

Samuel

clintrubber

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #7 on: February 15, 2011, 09:29:48 AM »

Quote
Can well imagine you sent your points to him as well, right? If so, please keep us informed about what you want to share of the subsequent discussion.

It is of course not only my decision what shall not be private anymore from a privat communication...

Samuel

Hi,

Ah, indeed, that would have better been formulated as: 'can share'.
OK, so you guys are indeed in contact with each other I understand.

Regards,

  Peter
« Last Edit: February 15, 2011, 11:03:26 AM by clintrubber »

sahib

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #8 on: February 15, 2011, 04:59:27 PM »
Thanks for your interest!

Quote
Sam, for some reason I can not open your link.

With a slow connection it might take a while, almost 1 MB. Other than that, I see no reason why it should not work--which Acrobat Reader version do you use? Have you tried copy the URL and pasting to a new browser window/tab?

You could also try the link from here: www.sg-acoustics.ch/analogue_audio/power_amplifiers/

I have a bullet speed comms yet I stil can't open it. I have tried the link on your site but it gives me a default of "This file can not be opened". Could that be the security of the stupid Windows 7? I'll try from the office tomorrow.

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #9 on: February 16, 2011, 04:32:32 AM »
Quote
I didn't see Cherry. I though he had a few interesting AES papers. IIRC in one he investigated how things like path impedance for power supply rail feeds and returns affect distortion in high power output stages. When investigating residuals as low as you are, there are many moving parts to consider.

Of course I did only consider references which are helpful for the topics covered but it is surely possible that I've missed a specific prior writing (happy to hear about that). PSRR/supply related distortion is actually covered by Self, at least to some extent, so didn't show up in my paper.

Quote
OK, so you guys are indeed in contact with each other I understand.

Sure, I did consider it fair to let him respond first before I made this public.

Quote
I stil can't open it.

Strange. Do you have the same problem with other PDFs from my site? I could forward it by e-mail of course.

Samuel


JohnRoberts

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #10 on: February 16, 2011, 10:52:10 AM »
Quote
I didn't see Cherry. I though he had a few interesting AES papers. IIRC in one he investigated how things like path impedance for power supply rail feeds and returns affect distortion in high power output stages. When investigating residuals as low as you are, there are many moving parts to consider.

Of course I did only consider references which are helpful for the topics covered but it is surely possible that I've missed a specific prior writing (happy to hear about that). PSRR/supply related distortion is actually covered by Self, at least to some extent, so didn't show up in my paper.

Samuel

I am not suggesting that Cherry offered any novel mechanisms, but IIRC there were a couple papers. One on output stage topology and practical difficulty to stabilize common collector vs. common emitter topology, and another on the ohmic contributions from things like wiring and PCB traces in high current push/pull audio circuits.

Nothing ground breaking but the only specific discussion of such things that I recall. They were published in the AES and not IEEE so somewhat lighter weight (FWIW, I haven't actually read Self's amp book, but i recognize his name from the audiophile designer community back in the day).

I'll let you decide if it (Cherry) is worthwhile looking at. I thought if it more because of the resolution floor in your measurements. Layout can matter if there are significant imbalances between push and pull stages. I guess if the layout and wiring are well matched, this is a non-issue and invisible, so only measurable with a bad layout, or very high resolution measurement tools.  Perhaps of only academic interest to designers, as a what not to do.   

I recall in designing power amps for silly high damping factor, even the speaker wire connector used on the output panel makes a measurable difference. So pushing measurement limits lower does expand the scope of design somewhat.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

robovox

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #11 on: February 19, 2011, 12:27:03 PM »
Self does in fact reference Cherry's May '81 JAES "A new distortion mechanism in Class-B amplifiers," which can be found in the library on Jan Didden's http://www.linearaudio.nl/ site.

Very interesting paper, Samuel, thanks for posting it.
« Last Edit: February 19, 2011, 12:33:15 PM by robovox »
I have an electric grandpa bed that talks to me while I sleep.
                                                              --Dean Venture

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #12 on: February 22, 2011, 01:45:54 PM »
Just noticed a subtle, but possibly evil drawing error in figure 57. The output of U2 should connect to Q13 base, not Q14 base. Q14 base should be grounded. Otherwise the polarity of the common-mode control loop is wrong and very large VAS currents will be enforced.

My apologies for this, I hope it did not so far, and will not in the future, cause any accidents. I uploaded a new PDF with a comment added; corrected schematic maybe later.

Samuel

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #13 on: February 24, 2011, 04:04:35 PM »
I've uploaded a new revision of the PDF which corrects figure 57. Otherwise there are no changes.

Samuel

hifizen

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #14 on: March 20, 2013, 02:20:24 PM »
Late to the party...  just found this paper last week wanted to say thanks Samuel for this excellent work!  Clearly, a lot of hard work and intellectual effort went into it.

Your paper has added by far the most substantial layer of new understanding to my knowledge of discrete op-amp design, since I read Doug Self's EW&WW articles on the sources of distortion in the mid-90's (15+ years later!).  I have a much better appreciation now for what's going on in the transimpedance stage, which in turn has germinated new thoughts on output stage design and compensation methods.

This has sparked in me a renewed interest in discrete design...  I was tempted to immediately go and pick up Doug's power amp book, but then noticed there is a 6th edition on the horizon.  So while I await his new edition (which will hopefully echo and expand on what you've written here), I bought Bob Cordell's book.  I've only skimmed a few sections so far, but it looks like a pretty good book.  I don't suppose you'll be commenting on Bob's book too?   ;)

OK, well in the meantime ...  I am working on a new discrete headphone amplifier design, and will be applying what you've written.  In particular, I'm rather smitten with the differential topology of fig 56, and will probably start with that if I can get a version working well in SPICE.  I will likely take up your suggestion to bootstrap the current mirror.  Any further observations about the properties of this topology - in particular, did you encounter any subtle / non-obvious attributes I should watch out for?

My hobby time is quite limited, but as I am able to make some progress on the design, I'll start a thread here to share what I learn...  Thanks again for putting generously sharing your thoughts on this.  It has been very inspirational.
- Chad.

ruffrecords

Re: Comments on Audio Power Amplifier Design Handbook by Douglas Self
« Reply #15 on: March 20, 2013, 06:17:05 PM »
Hi

Many contributors and readers of this forum will be familiar with D. Selfs writing (and those who are not should take actions to get!). In particular his audio power amplifier design handbook is already a classic. I did put together a paper with a couple of complementing and contrasting thoughts on the 5th edition. I hope you enjoy reading it and appreciate further conversation on the topics covered.

audio_power_amp_design_comments.pdf

Samuel

Just one comment on your comments.

There is no such thing as voltage feedback or current feedback. Both terms on their own are ambiguous.

Negative feedback can only be fully described by stating both the way it is derived and the way it is applied. So there are four types of negative feedback. All four types affect closed loop gain. How the NFB is derived affects output impedance (it can be lowered or raised) and the way the NFB is applied affects the input impedance (again it can be raised or lowered). The four types are:

1. Voltage derived and voltage applied
2. Voltage derived and current applied
3. Current derived and voltage applied
4. Current derived and current applied

The terms shunt or series derived and applied can also be used and can be more useful in describing the actual topology of the circuit. Unfortunately the correspondence between these terms and voltage and current derived/applied can be confusing.

I know this may sound like I have a bit of a bee in my bonnet about this and I suppose I have to some extent. It's just that I see the ambiguous terms voltage and current feedback bandied about all the time and it does nothing to improve the understanding of the average reader. And if you are going to critique someone else's work.....

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


 

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